This invention relates to a car navigation system for predicting the energy consumption of an automotive vehicle.
With the environmental problem becoming more and more serious, the efficient use of energy for vehicles is required. In view of this, demand has increased for an application of a car navigation system which can search for a route minimizing the energy consumption. Such an application requires a technique for predicting the amount of energy consumed along the route searched for. Incidentally, the energy consumption described herein includes the consumption of electric energy for an electric vehicle, the fuel consumption for a gasoline engine vehicle or a diesel engine vehicle and the amount of energy consumed by each motive power supply for a vehicle using a plurality of motive power supplies.
The factors determining the energy consumption of a vehicle are considered to include the landform, the traffics, the vehicle parameters, etc. Especially, the vehicle parameters have a great effect on the energy consumption, and therefore, are required to be reflected in the prediction of energy consumption. The vehicle parameters are considered to include the vehicle weight, the characteristics of energy consumption of the engine or the motor, as the case may be.
Roughly, two main methods are considered for predicting the energy consumption reflecting the vehicle parameters. One method is based on the actual energy consumption of a vehicle on the move. According to this method, the amount of energy consumed by a vehicle involved or a vehicle of the same type running along a road is recorded, and the energy consumption is predicted based on the record. Examples of this method are the inventions described in JP-A-2006-118479 and JP-A-2008-20382.
According to the other method, the energy consumption is predicted based on a physical model indicating the amount of energy consumed. In this method, the energy consumption is predicted for various models of vehicles, and therefore, the user is required to set, in the car navigation system in advance, the vehicle parameters required for energy consumption prediction. As one of the information indicating the energy consumption of a vehicle, the fuel consumption rate for emission test cycles is well known. The fuel consumption rate for emission test cycles is a measurement of the energy consumption of a vehicle running in a predetermined emission test cycle, and indicates the amount of energy consumed for a predetermined distance or the distance covered with a predetermined energy consumption. The procedure for emission test cycle and the fuel consumption rate for the emission test cycle are in public domain, and therefore, the user can predict the energy consumption by multiplying the distance to be covered.
In the method of predicting the energy consumption based on the actual energy consumption of a vehicle on the move, the energy consumption can be predicted only for a road on which the running result for the vehicle involved and other vehicles of the same model as the vehicle involved can be obtained. In some cases, therefore, the route for minimum energy consumption may not be found.
In the case where the energy consumption is predicted using a physical model, on the other hand, the user is required to set the vehicle parameters in advance for the vehicle involved as described above. It is difficult for the user, however, to set the parameters for the engine or the motor which requires the special knowledge, and the user has no choice but to set the vehicle parameters based on the information generally available from the catalog of the vehicle involved or the information acquired from the sensors mounted on the vehicle.
The generally available information on the vehicle energy consumption includes the emission test cycle fuel consumption rate used conventionally, and based on this information and the distance covered, the energy consumption can be predicted. The emission test cycle fuel consumption rate, however, represents the value of energy consumption for the distance covered according to a prescribed emission test cycle procedure, and therefore, a highly accurate prediction value reflecting the landform and the traffics along the running route cannot be obtained from the value of the emission test cycle fuel consumption rate. Thus, the problem is posed that it is difficult to search for a route minimizing the energy consumption accurately.